Measuring the electric field produced by corona discharge in rod-plate air gaps by using E-FISH method

Electric field measurement is one of the key challenges in plasma diagnostics. Currently used techniques are either limited by the sensor material and size, which will distort the measured E-field distribution, or limited by the photon emission, which is difficult to be applied in various plasma measurements. The Efield diagnostic technique based on the field-induced second-harmonic (E-FISH) has the advantages of high temporal and spatial resolution and non-invasive measurement. It has a broad application prospect in plasma diagnosis. Previous E-FISH-based E-field measurement studies relied on the plane-wave approximation of the probe laser, which introduced spatial averaging errors in the electric field. This paper develops a method to accurately obtain the spatial distribution of the plasma E-field by applying a focused Gaussian beam. The two-dimensional distribution of the e-field of a positive corona discharge in a centimeter-scale rod-plate gap is measured empirically, and a two-dimensional corona model is developed to validate the results. The measurement results show that the surface E - field of the rod electrode is suppressed by the positive ions, and the E-field at both the migration zone and the surface of the plate electrode obtain a significant enhancement. The work in this paper provides a new way for high spatial resolution of E -field distribution measurement for plasma diagnostics.